This open-label, investigator-initiated study uses the new antiretroviral nucleoside, 1592U89 to examine the comparative differences in CSF vs. plasma in: (1) kinetics of viral responses, (b) the decrement of immune activation markers, and (c) drug levels with the principal focus on patients with severe AIDS dementia complex (ADC). This study uses 1592U89, which has favorable characteristics for treating CNS infection, as a probe to extend understanding the pathobiology and treatment of infection of the nervous system. It aims to characterize the magnitude and time course of CNS treatment effect in a group of patients with local CNS infection and consequent clinically important neurological disease. This is a virological, immunological, and pharmacokinetic study which will only secondarily obtain preliminary clinical efficacy data. Nonetheless, these data should provide important background related to defining the overall utility of this drug both in treating and preventing ADC and in interrupting the 'reseeding' of systemic infection by resistant virus from the CNS.